In manufacturing of a semiconductor device or an LCD substrate, a technique called “photolithography” is used to form a resist pattern on a substrate. Photolithography refers to a technique that coats a semiconductor wafer (hereinafter referred to simply as a “wafer”) with a resist liquid, exposes the resist in a predetermined pattern, and then develops the resist, thereby to form a desired resist pattern. Such a process is generally performed in a system made up of a coating-and-developing apparatus for coating and developing a resist liquid and an exposure apparatus connected to the coating-and-developing apparatus.
In recent years, there has been an increasing tendency to reduce the size and film thickness of device patterns. Accordingly, the demand for enhanced exposure resolution is increasing. To meet this demand, a technique is proposed to improve the conventional exposure method that uses argon fluoride (ArF) or krypton fluoride (KrF). This technique exposes a substrate after forming a light-transmissive liquid layer (e.g., a deionized water film) on its surface (which is hereinafter referred to as ‘immersion exposure’). This immersion exposure technique utilizes the fact that the wavelength of light decreases in water; ArF (light) actually has a wavelength of 134 nm in water though its normal wavelength is 193 nm.
An immersion exposure apparatus will now be briefly described with reference to FIG. 21. A wafer W is held in a horizontal attitude by a retention mechanism (not shown). An exposure means 1 is disposed above the wafer W such that the exposure means 1 faces the wafer W across a gap. A lens 10 is provided in the center portion of the leading end of the exposure means 1. Outside the lens 10 are provided a supply port 11 for supplying deionized water to the surface of the wafer W and a suction port 12 for sucking and thereby retrieving the supplied deionized water. The deionized water continuously supplied through the supply port 11 is continuously retrieved through the suction port 12, thereby forming a liquid film (or a deionized water film) between the lens 10 and the surface of the wafer 10. The wafer W is irradiated through the lens 10 and the liquid film with light emitted from a light source (not shown) to imprint a predetermined circuit pattern in a resist R.
Upon completion of the exposure of one imprint region (or shot region) 13, the exposure means 1 is moved in a horizontal direction to align with and expose the next imprint region 13 while maintaining the liquid film between the lens 10 and the surface of the wafer W, as shown in FIG. 22. This process is repeated to imprint a predetermined circuit pattern in the surface of the wafer W. It should be noted that in FIG. 22 each shot region 13 is shown larger than actual size.
The above immersion exposure technique has a problem in that the resist might be dissolved into the liquid film and the dissolved components, for example, PAG (acid generator) or a quencher, may remain on the wafer W. Although a process for removing the liquid on the surface of the wafer W is performed after the exposure process, the liquid may possibly be left on the surface. Especially, since the peripheral edge portion of the wafer W has a beveled shape, there is the possibility that a liquid containing the above dissolved components may remain on the beveled surface of the peripheral edge portion of the wafer W.
If liquid containing the above dissolved components remains on the wafer W, the dissolved components adhere to the wafer W and may cause generation of particles, resulting in defects in the resist pattern and hence in the device. Furthermore, these particles may adhere to the wafer transfer arms installed in the coating-and-developing apparatus and, as a result, may be scattered in processing units or transferred to another wafers, thus causing “particle contamination”.
When particles originating from the dissolved components are attached to the wafer W, these particles are fixedly or firmly adhered to the wafer during the heat treatment performed after the exposure process, affecting the line width of the pattern. Furthermore, the particles adhered to the wafer W may damage the pattern during the developing process.
Efforts have been made to develop a new resist liquid insoluble in the liquid film formed during the immersion exposure process. Further, it has been proposed that a water-shedding protective film may be coated onto the resist film in order to reduce the dissolution of the resist into the liquid film and to prevent the liquid used in the immersion exposure process from remaining on the surface of the wafer W. However, it is very difficult to create such a new resist liquid. Further, adding a protective film forming step results in the increase in the total number of processes and hence in cost.
In view of the above, a practical method for removing the particles originating from the resolved resist liquid components is to clean the surfaces and the peripheral portion of the wafer W after the immersion exposure process. The so-called spin cleaning apparatus is generally used as a unit for cleaning the wafer W. This apparatus rotates the wafer W while supplying a cleaning liquid to the center portion of the wafer W, and thereafter performs spin-drying. This unit is incorporated in the coating-and-developing apparatus.
However, such a cleaning apparatus requires a spin chuck for rotating the wafer W and a large cup for recovering the cleaning liquid scattered from the wafer W. This means that the entire cleaning apparatus has a large size and a complicated structure. Furthermore, if the cleaning apparatus is provided with a suction device ensuring that the cup assuredly captures the scattered cleaning liquid, the size of the cleaning apparatus becomes larger.
JP5-291223A discloses a cleaning apparatus that has neither a rotating mechanism nor a cup member for recovering the cleaning liquid. This cleaning apparatus includes a cleaning chamber and a buffer tank each including a heat exchanger with heating and cooling capabilities. A cleaning liquid is supplied from the buffer tank to the cleaning chamber through a substantially center portion of the cleaning chamber to clean the wafer W, and the supplied cleaning liquid is discharged through the discharge port provided in the lower center portion of the cleaning chamber and returned to the buffer tank.
In the cleaning apparatus disclosed in JP5-291223A, the cleaning liquid is sprayed onto the center portion of the wafer W to clean the surface of the wafer W. The cleaning liquid that has dropped from the surface of the wafer W flows into the discharge port and is trapped in the buffer tank. However, it is difficult for this cleaning apparatus to uniformly spray a cleaning liquid over the entire surface of the wafer W and thereby to reliably clean both the surface and the peripheral portion of the wafer W. Therefore, this cleaning apparatus is not suitable for the cleaning performed after the immersion exposure process.